Assessment of the Adequacy of the Reproduction of Surface Water Transformation by Different Cmip6 Models in the North Atlantic

This article discusses the correctness of the reproduction of density fluxes and transformation of surface waters in the North Atlantic by models from the CMIP6 project. The transformation of surface waters in the North Atlantic is closely related to convective processes and the formation of modal waters. These processes are part of the Atlantic Meridional Circulation Cell and the global conveyor belt as a whole. This study uses NCEP CFSR/CFSv2 reanalysis data as the most reliably reproducing the interaction between the ocean and the atmosphere. For comparison, data from the historical experiment of the INM-CM-5.0, MPI-ESM1.2 and MIROC6 models from 1979 to 2014 were taken. All models generally reproduce the seasonal dynamics of density and transformation flows, which depend primarily on heat flows. The models reproduce a positive density flux in winter in the North Atlantic with a maximum near the Gulf Stream. Next, based on TS-analysis, individual surface water masses were identified and the climatic dynamics of transformation rates were analyzed. The transformation rate of individual water masses is most near to CFSR values reproduced by the MPI model, less accurately by MIROC6; the greatest differences with the CFSR reanalysis are reproduced by the INM model.